The present invention is directed to an improved heat sensitive coating composition and heat sensitive paper for thermal printing devices containing the composition. The composition is particularly well suited for heat sensitive paper used in high speed facsimile copiers.
In the past several years, facsimile copiers have become a popular way of transmitting print messages between remote locations over telephone lines. Due to the high speed at which facsimile copiers operate, high quality thermal responsive recording paper is required to provide clear reproduction of the transmitted images.
In our previously granted U.S. Pat. No. 4,289,535, the disclosure of which is hereby incorporated by reference, there is disclosed a heat sensitive composition comprised of a chromogenic basic triphenylmethane dyestuff and an acidic phenolic color-developer in a carrier composition. More specifically, the triphenylmethane dyestuff is a 3,3-bisarylphthalane derivative and the color-developer is a bisphenol such as bisphenol A (4,4'-isopropylidenediphenol). The carrier for the dyestuff and color-developer is a mixture of a water soluble anionic polysaccharide gum, such as gum arabic, and sucrose benzoate which functions as a stabilizer.
U.S. Pat. Nos. 4,138,357 and 4,399,188 disclose heat-sensitive compositions containing a thermochromic dyestuff and an ester of hydroxybenzoic acid as the color-developer.